Apparatus for use with tone producing devices



y 1957 B. FAUST APPARATUS FOR USE WITH TONE PRODUCING DEVICES Filed July 18, 1955 3 Sheets5heet 1 INVENTOR.

A flame s y 1957 B. F AU ST APPARATUS FOR USE WITH TONE PRODUCING DEVICES Filed July 18, 1955 3 Sheets-Sheet 2 INVENTOR.

Berna/p Faust BY Curl/s, Moms 850ff0rd B. FAUST May 28, 1957 APPARATUS FOR USE WITH TONE PRODUCING DEVICES Filed July 18, 1955 3 Sheets-Sheet 3 IN VEN TOR.

m m Wm 05 a 0 5 m mm 8 fl w A f/omeys United States Patent APPARATUS FOR USE WITH TONE PRODUCING DEVICES This invention relates to electric organs and similar tone-producing devices. More particularly, this invention relates to apparatus adapted for use with such devices to produce sound effects simulating the tonal quality of percussive instruments.

For some time now, there has been extensive use of musical instruments arranged to produce audible tones by electrical means. Predominant among these instruments is the electric organ, which includes apparatus for generating a plurality of constant amplitude, audio-frequency electrical signals; a piano-like keyboard and, frequently, a set of foot-pedals, for selecting the desired combination of signals; and audio amplification means to intensify the selected signals so that they may be converted into audible sound signals of proper amplitude by a loudspeaker or similar transducing device. Electric organs further generally include a series of manually operable drawbars or tabs which are arranged to control the harmonic content of the signal produced by depression of the keys, so that any one of a variety of tonal qualities may be obtained as desired. Commonly, the electric organ also will have an upper and a lower keyboard (known as manuals), one for each hand, and the harmonic content of the signals controlled by either keyboard may be pre-set, independently of the other keyboard, by manipulation of appropriate drawbars or tabs.

Although such electric organs are adapted to produce sound tones effectively simulating many ordinary types of musical instruments, such as Woodwinds, brass, etc., the simulation of percussive instruments, such as a banjo or bass-fiddle, has presented a special problem in that the desired tone is not of constant amplitude. Various attempts have been made to solve this problem, but the apparatus available heretofore has been unsatisfactory in many respects.

Accordingly, it is an object of this invention to provide apparatus, for use with electrical tone-producing devices, which makes possible the production of tonal effects closely simulating those produced by percussive type in struments. It is a further object of this invention to provide such apparatus that may readily be installed in standard organs as an accessory thereto without requiring additional keyboards. Other objects, advantages and as pects of the present invention will be partly apparent from, and partly pointed out in, the following specification considered together with the accompanying drawings, in which:

Figure l is a schematic diagram representing one embodiment of the present invention;

Figure 2 is a schematic diagram showing a further as pect of the present invention; and

Figure 3 is a schematic diagram showing a still further aspect of the present invention.

In electric organs now commonly in use, individual tone generators (such as an oscillator or similar device) 70 are employed to produce each of the audio-frequency signals corresponding to the notes within the range of the instrument. When any key on the keyboard is depressed, an audio-frequency signal corresponding to the desired tone is transmitted from the respective generator, through amplification equipment (typically comprising a pre-amplifier and a power amplifier), to a loudspeaker device. See, for example, U. S. Patent No. 2,681,585, issued to J. M. Hanert on June 22, 1954. If the drawbars have been set to give a chosen harmonic content to the tone (i. e. tone color), the audio-frequency signals produced by two or more of the generators will be combined in predetermined amplitude ratios, and the resulting composite tone will be amplified and fed to the loudspeaker.

In accordance with one aspect of this invention, the apparatus described herein includes an input circuit which is connectible to a standard electric organ at a point in the sound channel where this composite tone exists as a constant-amplitude electrical signal, and an output circuit in which is produced an output signal having the same harmonic content as the electrical input signal but varying in amplitude in accordance with the decay characteristics of the percussive instrument to be simulated. This output circuit is connectible to the organ amplification equipment so as to feed the percussive tone at a suitable signal level to the organ loudspeaker.

Referring now to the upper left-hand corner of Figure 1, there is shown an audio transformer generally indicated at 10 having a secondary winding 12, and which represents a transformer such as might be used in the main sound channel of a standard electric organ, e. g. immediately preceding the organ preamplifier. The composite audio-fre uenc signal roduced b the electric or antone-generating equipment is coupled to this transformer, as by primary winding means not shown herein, and produces a corresponding tone signal in the secondary Winding 12. The lower terminal 14 of this winding is connected to the common circuit ground G, while the upper terminal 16 is connected through a resistor 18 to the control grid 20 of an amplifier tube generally indicated at 22, and also is connected through a resistor 24 to ground G. The control grid 22 is shunted to ground through a small capacitor 26.

The cathode 28 of this tube 22 is connected in the usual way through a small biasing resistor 30, in parallel with a by-pass capacitor 32, to the ground G, and also is connected to the suppressor grid 34 of this tube. The anode 36 of this tube is connected through a load resistor 38, and a high-voltage lead 40, to the positive terminal 42 of a D.-C. power supply, generally indicated in block form at 44, which is energized by the usual A. C. power line (e. g. volts, 60 cycles), and the neutral terminal 46 of which is connected to ground G. This power supply may be any one of the usual types employed for providing operating potentials for audio amplifiers and similar devices and may, for example, furnish a positive potential of 200 volts to ground at its terminal $2. The screen grid 48' of the tube 22 is connected through a decoupling capacitor 50 to ground, and also through a series resistor 52 to the high-voltage lead 4'9.

The audio-frequency signal coupled from the transformer 10 to the tube 22 thus appears on the anode 36 of this tube in amplified form, and is fed through a coupling capacitor 54, to the control grid 56 of a second amplifier tube generally indicated at 58. This amplified signal also is fed along a lead 60 down to one end of a potentiometer 62, the remote end of which is grounded. It will thus be apparent that the amplified composite tone signal, of constant amplitude, is fed into two separate channels. The latter channel (i. e. through the potentiometer 62) constitutes a sound channel, while the former (i. e. through the second amplifier tube 58) constitutes a control channel, and includes special circuitry adapted to vary the amplitude of the signal passing through the sound channel, in a manner to be explained hereinbelow, so as to produce an output signal simulating the desired percussive sound effect.

The signal on the movable arm 66 of the potentiometer 62 is connected through a capacitor 64 to a first control grid 68 of a multi-element amplifier tube (e. g. to grid No. 3 of a type 6L7 control tube) generally indicated at 70. The cathode 72 of this latter tube is connected through a biasing network comprising two series resistors 74 and 76, both in parallel with a bypass capacitor 78, to the common ground G. The common connection point between these latter two resistors 74 and 76 is returned through a grid-return resistor 80 to the first control grid 68 to establish proper bias on this grid. The cathode 72 of this tube also is connected, in the usual manner, to the suppressor grid 82 of the tube.

The anode 84 of this tube 70 is provided with proper operating potential by a connection through a load resistor 86 and a filter network, comprising a shunt capacit'or 88 connected to ground G and a series resistance element 90, to the high-voltage lead 40 and thence to the positive terminal 42 of the D.-C. power supply 44. The screen grid 92 of this tube is connected through a tie-coupling capacitor 93 to ground, and is provided with operating potential by a connection through a series resistance 94 to the above described filter network. This screen grid also is connected through a resistor 96 to the cathode 72 of this tube 70.

The audio-frequency signal appearing on the anode 84 of this latter tube 70 is coupled through a capacitor 98 to one end of a potentiometer 100, the remote end of which is grounded. The movable arm 102 of this potentiometer is connected to one output terminal 104, while the other output terminal 106 is grounded. By means not shown herein, these output terminals are adapted to be connected to the organ amplification equipment (e. g. connected to the input circuit of the usual pre-amplifier), to produce an audible signal in the organ loudspeaker.

Reverting now to the control channel mentioned hereinabove, the cathode 108 of the amplifier tube 58 is connected to ground through the usual biasing network comprising a small resistor 110 in parallel with a bypass capacitor 112, and the control grid 56 is connected to ground through a grid-return resistor 114. The anode 116 of this tube is supplied with operating potential through the primary winding 118 of an audio transformer, generally indicated at 120, the remote end of the primary winding being connected to the high-voltage lead 40. The audio-frequency signal developed on the anode of tube 58 consequently appears on the secondary winding 122 of this transformer, and is fed therefrom to a full-wave rectifier circuit to produce a correspondingv D.-C. signal.

For this purpose, the upper end (as viewed in the drawing) of the secondary winding 122 is connected to one electrode of a first rectifier 124, and also is connected to one electrode of a second rectifier 126 which is poled oppositely to the first rectifier. Both of these rectifiers preferably are of the dry type. The other electrodes of these rectifiers are connected together through two energy-storage capacitors 128 and 130, and the common connection between these capacitors is returned to the lower end of the secondary winding 122. With this arrangement, the audio-frequency signal appearing across the secondary winding 122 produces a D.-C. voltage across the two series-connected capacitors 128 and 130 and the loadresistor 132 connected in parallel therewith.

The D.-C. signal thereby produced is fed through a filter network comprising two series resistance elements 134 and 136, and two shunt capacitive elements 138 and 140. Connected in parallel with the latter shunt capacitor 140 is an output resistor142.

V Theright-hand end (as viewed in the drawing) of this v 4 latter resistor 142 is connected to the control grid 144 of a triode tube generally indicated at 146. The lefthand end of the resistor 142 is connected, through a lead 148, to the cathode 150 of this tube. Thus, the D.-C. voltage produced by the full-wave rectifier circuit is applied directly across the input circuit of the tube 146. The anode 152 of this tube is connected through a resistor 154 (e. g. having a resistance of 30 to 60K ohms) to the common system ground G.

The cathode 150 of this tube 146 is connected through a relatively large resistor 156 (e. g. having a resistance of 12 megohms) to the negative terminal 158 of the D.-C. power supply 44. This terminal 158 may, for example, furnish a negative potential of volts to ground. A series of charging capacitors 160, 160a, 16% and 160C, of difiering capacitance values, also are connected to the cathode 150, and their remote plates are connected, respectively, to corresponding terminals of a rotary step switch, generally indicated at 162. The movable arm 164 of this step switch is returned directly to ground G.

In operation, when there is no audio-frequency tone signal being fed to the input transformer 10, the control grid 144 and cathode of the triode tube 146 will be at substantially the same potential since no D.-C. voltage will be developed by the full-wave rectifier circuit. Further, these electrodes will be negative relative to the anode 152 of this tube, since this anode is effectively at ground potential. Consequently, the tube 146 will tend to conduct current heavily, the current path being traced from the neutral terminal 46 of the D.-C. power supply 44 to ground, through the resistor 154 to the tube anode 152, through the tube 146 to the cathode 150 thereof, through the large resistor 156 and back to the negative terminal 158 of the D.-C. power supply.

Because the impedance of resistor 156 is considerably greater than the internal impedance of the tube 146 when its cathode and grid are at substantially the same potential, a large portion of the voltage drop in the abovedescribed current path will be across the resistor 156. Thus, the cathode 150 of tube 146 will, in this condition, be only somewhat negative with respect to ground G. This cathode is connected directly, by a lead 166, to a second control grid 168 (e. g. grid No. l of a 6L7) of the multi-element tube 70 referred to previously. With the triode tube 146 conducting, the potential thus applied to this second control grid 168 by the cathode 150 is of such a magnitude that the multi-element tube 70 serves as an amplifier, and develops on its anode 84 an audio-frequency signal in accordance with any input signal applied to its first control grid 68.

The apparatus described above operates in the follow- 1 ing manner: When a player presses a key or foot-pedal to produce a percussive tone, the organ tone generators feed a constant-amplitude audio-frequency signal to the input transformer 10. This signal activates the control channel, and produces almost immediately a negative pulse of D.-C. voltage at the output of the full-wave rectifier circuit, i. e. across the output resistor 142. This voltage pulse, in turn, makes the control grid 144 of the triode tube 146 negative wtih respect to the cathode 150 of this tube, and is of sufficient magnitude to cut this tube otf completely.

The cathode 150 cannot, however, instantaneously go fully negative with respect to ground because this cathode is coupled to ground through one of the charging capacitors 160. Consequently, the selected one of these capacitors starts to charge up immediately when the tube 146 is cut off, and the voltage on the cathode 150 thus becomes more negative at an exponential rate determined by the relative Parameters of the selected capacitor and the resistor 156. correspondingly, the potential of the second control grid 168 of the tube 70 in the sound channel becomes more negative exponentially, thereby gradually decreasing the gain of this amplifier stage until the tube 70 no longer produces an appreciable audiofrequency signal on the anode '84 thereof in accordance with the signal on the first control grid 68.

Therefore, immediately after the player depresses the key, the organ loudspeaker will produce a tone of usual strength and having the desired harmonic content. This tone then drops off rapidly in amplitude until it disappears completely. It has particularly been found that the decay characteristics produced by a capacitor-resistor charging circuit, such as described, produces a tone in the organ loudspeaker very closely approximating the tonal quality of real percussive instruments, and that the effect is especially pleasing to the ear. Further, the charging capacitance may be varied by the step switch 162 in order to select the decay rate comparable to the percussive instrument to be simulated.

When the player releases his key, the triode tube 146 will commence to conduct almost immediately, and the selected capacitor 160 will therefore discharge to permit the second control grid 168 of the tube 70 to return to the potential required for operation of this latter tube. The capacitor 160 will discharge very rapidly, since the current path for discharge is through the triode tube 146 which has a low internal impedance relative to the resistor 156. The resistor 154 is connected between the anode 152 of the tube and ground to prevent the capacitor 160 from discharging too rapidly, which might produce an annoying click in the organ loudspeaker. However, the capacitor discharges sufficiently rapidly to reset the percussive unit well before the next key is depressed.

It will, of course, be apparent, that various switching controls (not shown) may be provided for the organ player so that he may connect the percussive unit described into the organ sound channel when desired, or may connect it so that it operates on only one of the keyboards or only on the foot-pedals, leaving the remainder of the organ in condition to produce constant amplitude tones in the usual manner.

With the above-described arrangement for producing percussive tonal effects, the player must release the played key before depressing another key, in order to permit the percussive unit to recondition itself for the next note. This detached form of playing is fully satisfactory for the simulation of many kinds of percussive instrumentations, but it sometimes is desirable, nevertheless, to be able to produce a second percussive note while a first key is held down, or to produce several percussive notes in quick succession with zero time interval between releasing one key and pressing the next. This problem is solved in accordance with a further aspect of the present invention described hereinbelow.

Referring now to Figure 2, at theleft-hand edge thereof is a series of terminals 200 (with differentiating suffixcs), each of which represents, in an electric organ, an individual connection point where there exists an electrical audio-frequency signal produced in accordance with the depression of any one key (or foot-pedal). That is, when the organ player depresses a single key, a corresponding audio-frequency signal is arranged to be fed, say; to terminal 200a. And if, at the same time, a second key is depressed, a signal corresponding to the note represented by the second key will be fed to, say, terminal 200]). These signals may, in the usual way, include any desired harmonic components in accordance with the setting of the organ drawbars.

It is to be understood, of course, that the total number of these terminals 200 normally will be equal to the number of keys. on one organ keyboard, and is not necessarily limited to the number shown in the drawing. Further, to provide a schematic indication of the connections between these terminals 200 and the corresponding organ sound channels, the upperfive of these terminals (as viewed in the drawing) are shown connected by individual leads to the respective output circuits of five tone generating devices, generally indicated within blocks 190, 191, 192,

193 and 194. Each of these generating devices is controlled by a corresponding switch 195, 196, 197, 198 and 199, each of which, when actuated in response to the depression of a corresponding key on the organ keyboard, completes a circuit to ground G to cause the associated generating device to transmit an audio-frequency signal to the respective one of the input terminals 200. Only five such connections to the organ sound channels are shown, in order to simplify the drawing, it being understood that the other terminals are similarly connected to corresponding organ sound channels each activated in response to depression of one of the keys.

The central fourteen of these terminals (i. e. terminals 200a to 20011) are connected, respectively, by corresponding leads 202, 2021), etc., to individual percussion units, generally indicated by blocks 2041:, 204b, etc., and each of which is identical to the percussion unit previously described and shown in Figure 1. Each of these terminals 200a through 20021 may, for example, be connected to a corresponding percussion unit input terminal represented by the reference numeral 16 of Figure 1. (No connecting lead is shown in Figure 2 for the other percussion unit input terminal 14 of Figure 1, it being understood that there are common ground connections between the various percussion units and the organ signal generating apparatus for this purpose.) The output circuits of the percussion units 204 are connected, respectively, to corresponding isolation resistors 206a, 206b, etc. (e. g. by a connection from the output terminal identified in Figure l by the numeral 104). Each resistor may, for example, have a resistance of one megohm.

The remote ends of the upper seven isolation resistors 206:: through 206g are connected together and, through a coupling capacitor 208, to one control grid 210 of a dual-purpose amplifier tube, generally indicated at 212, and which serves as a mixer stage to combine the various percussive tones produced by the units 204a, 204b, etc. The remote ends of the lower seven resistors 206/1 through 20611 are similarly connected together, and, through a coupling capacitor 214, to the second control grid 216 of the tube 212. Each of these control grids 210 and 216 is returned to ground through a corresponding grid-return resistor 218 and 220; the common cathode 22 of this tube is connected to ground through a small bias resistor 224 in parallel with a by-pass capacitor 226.

The two anodes 228 and 230 of this tube 212 are connected together through a pair of load resistors 232 and 234, in series, the common connection 236 of which is returned through a filter resistor 238 to the positive terminal 240 of a D.-C. power supply generally indicated by the block 242; a filter capacitor 244 also is connected between ground 6 and this common connection point 236. The power supply 242, which may be of any type commonly employed for providing suitable operating potentials for audio amplifiers, etc., is energized by the A.-C. power line, e. g. volts, 60 cycles, and its negative terminal 246 is connected to ground G.

The remote ends of the load resistors 232 and 234 are connected together through two output resistors 248 and 250, in series, the common connection 252 of which is connected through a coupling capacitor 254 to one end of a potentiometer 256, the remote end of which is grounded. The movable arm 258 of this potentiometer is connected directly to one output terminal 260, while the other output terminal 262 is grounded. These two output terminals are, in turn, connected (by means not shown herein) to the organ loudspeaker system, e. g. through the usual organ pre-amplifier and power amplifier.

Thus, when the player depresses a key corresponding to, say, terminal 200a, this terminal will be supplied with a constant-amplitude, audio-frequency signal having the desired harmonic content. This signal will pass into the corresponding percussion unit 2040, where it will be operated on in the manner described hereinabove to produce in the output circuit of this latter unit a percussive-type tone with the appropriate decay characteristics for the instrument to be simulated. This percussive tone is fed through the isolation resistor 206a to the dual-purpose mixer tube 212, which produces a corresponding percussive tone, across the output terminals 260 and 262, which is transmitted in the usual way to the organ loudspeaker for conversion to the desired sound effect.

If the player depresses a second key, e. g. corresponding to input terminal 200b, while still holding down the first key, this input terminal will similarly be supplied with a constant-amplitude tone, but of a different basic frequency than that supplied to terminal 200a. The tone supplied to terminal 200]; will pass through the corresponding percussive unit 20412 to produce a percussive-type tone which is fed through the mixer tube 212 to the organ loudspeaker as previously described. Since the two tones hereinabove referred to pass through different percussion units (i. e. 2040 and 20 1b), the need for detached playing is obviated; that is, one key may still be held down (not released) when the second key is struck and yet the percussive note of the second key will sound at full strength.

The fourteen input terminals 200a through 200 of the composite percussive system shown in Figure 2 are connected (by means not shown) to those organ sound channels corresponding to fourteen consecutive keys of only one of the two keyboards typically used on electric organs. The sound channels corresponding to the keys on either side of the selected fourteen keys are connected to other input terminals of this system (such as are identified by the numerals 200a, 20017, 200a, 20011, etc.), which in turn are connected to a corresponding one of the cen tral fourteen terminals 200a, etc. That is, terminal 200a is connected to terminal 200a, so that the tone produced by the key corresponding to terminal 200a will be fed through the percussive unit 2040, and thence to the organ loudspeaker. Similarly, terminal 20Gb is connected to terminal 200b, terminal 20011 is connected to terminal 200n, etc.

Only fourteen separate percussive units are provided because the hand spread of the organ player normally cannot encompass more than fourteen consecutive keys. Thus, it will be impossible for the fingers of one hand to depress, at the same time, two keys the corresponding tone signals of which would pass through the same percussive unit 204a, etc. Such an arrangement, of course, afiords substantial economy of parts. I

Some existing organs are arranged in such a manner that the output signal produced by depression of any single key is not available separately from the output ignals of the other keys in the same manual, i. e. in such organs the output signals for all keys of a manual are combined at a single common point. It has been found that such organs may readily be adapted for nondetached playing of percussive tones by means of the circuit arrangement shown in Figure 3.

In Figure 3, the output signal produced by depression of any of the keys in a manual is fed (by the usual organ circuitry not shown herein) to an audio transformer a and develops an alternating voltage in the secondary winding 12a thereof. One end of this secondary winding is grounded at G, and the other end is connected to a common lead 300 which, in turn, is connected to the movable arm of each one of a series of switches 3 32a, 3021), etc. Each of these switches is actuated by depression of a corresponding organ key, and for this purpose the switches may, for example, be mounted adjacent the keys either internally or externally of the organ housing.

As in the composite system of Figure 2, 14 separate percussive units 304a through 30411 are provided, the input circuit of each being connected to the fixed contact of a respective one of the switches 302a through 30211. Also similar to the arrangement of Figure 2, the fixed contacts of the switches on either side of the central group of 14 are connected to the input circuits of corresponding per,

cussive units, i. e. switch 302m is connected to percussive unit 30411, switch 302a is connected to percussive unit 304a, etc. i

These percussive units may be identical to the circuitry described with reference to Figure 1. Or, to economize on components, the amplifier stage formed by tube 22 of Figure 1 may be omitted from each percussive unit, and one such amplifier stage may be inserted between the transformer secondary Winding 12a and the common lead 300 if the additional amplification is required for the particular organ involved.

The output circuits of each percussive unit 304a, 304b, etc. again are coupled through corresponding isolation resistors 306a, 3061;, etc., and capacitors 308 and 310 to mixer stage generally indicated within the block 312 and which may be identical to the mixer circuitry described with reference to Figure 2. As before, the percussive tones developed in the output of the mixer are fed through conventional organ amplification equipment, comprising a pro-amplifier 314 and a power amplifier 316, to the organ loudspeaker 318.

It will be apparent that in the Figure 3 arrangement each individual percussive unit i normally disconnected from the organ sound channel and is activated only when a key corresponding to that unit is depressed. To assure tie-activation until a key is struck, each unit may additionally be provided with an audio-frequency shortcircuit across its input terminals, the short-circuit beingremoved by the opening of a set of switch contacts (not shown) which open when the corresponding key is struck.

In operation, when a key is struck, e. g. the key corresponding to switch 302a, the constant-amplitude audiofrequencysignal generated by the organ is fed through the upper percussive unit 304a to produce in the output thereof an exponentially-decaying tone simulating the desired percussive effect. This tone signal passes through the mixer stage 312, the amplifiers 314 and 316, and produces a corresponding audible tone in the loudspeaker 318. If a second key is struck, e. g. corresponding to switch 30211, at the same instant the first key is released, the second signal will pass through switch 302b, the next percussive unit 3041;, and produce a corresponding percussive tone in the organ loudspeaker. Since the two signals pass through different percussive units, the player need not delay between releasing the first key and depressing the second key to permit the percussive circuitry to reset itself.

If the second key is struck while the first key still is held down and after the first percussive tone has died out, the loudspeaker will produce two percussive tones corresponding to the two keys held down just as though both keys had been depressed simultaneously. This will occur because though the tone produced by the first percussive unit 304a had faded out, the audio-frequency signal corresponding to the first key still is present on the common lead 300 and will pass through the second percussive unit 304b when the second key is struck. Normally, of course, the first key will not be held down continuously while the second key is struck, and so such an effect will not typically be encountered. Nevertheless, the appearance of both tones when the second key is struck may be desired, and in accordance with the arrangement described such an effect is available at the option of the player by continuing to hold down the first key. It may also be noted that upon releasing only the first key, the tone corresponding thereto will immediately disappear and the tone from the second key will continue to fade out percussively through the action of its corresponding percussive unit as though the first key had never been struck. The player therefore can choose to carry over the first tone for as long as desired or not at all by releasing the first key when the second is struck.

When a group of percussive units is used as described with reference to Figures 2 and 3, it is advantageous to provide means for changing the fade-out characteristics of the various units simultaneously with a single control. This may be done, for example, by ganging the step switches 162 (referring to Figure 1) of each unit so that all of these switches are operated together.

Although specific preferred apparatus illustrative of the invention has been set forth in detail, it is desired to emphasize that this is not intended to be exhaustive or necessarily limitative; on the contrary, the showing herein is for the purpose of illustrating the invention and thus to enable others skilled in the art to adapt the invention in such Ways as to meet the requirements of particular applications, it being understood that various modifications may be made Without departing from the scope of the invention as limited by the prior art.

I claim:

For use with an electnic organ of the type wherein constant-amplitude, audio-frequency signals are produced in selected harmonic combinations by depressing one or more manually-operable keys, and wherein said audiotrequency tone signals are to be converted to audible sound signals for listening pleasure, apparatus for transforming said constant-amplitude signals to variable amplitude signals simulating the tonal etfect of percussive instruments, comprising, in combination, an input circuit adapted to be coupled to the tone-generating portion of said musical instrument to receive a constant-amplitude audio-frequency signal therefrom, circuit means comprising a sound channel and a control channel coupled to said input circuit, alternating-current rectifying means forming part of said control channel and adapted to produce a pulse of direct-current voltage substantially simultaneously With the receipt of a tone signal in said input circuit, resistance-capacitance discharge means for producing an exponentially-varying control signal upon initiation of a tone signal in said musical instrument, electronic switch means coupled to said rectifying means and arranged to activate said discharge means in response to said directcurrent voltage pulse, signal-varying means forming part of said sound channel and coupled t said input circuit, said signal-varying means being under the control of said discharge means and arranged to alter the amplitude of the signal fed to said signal-varying means in accordance with the changing magnitude of said control signal, the variation in magnitude of said control signal being such as to cause the amplitude of said tone signal to decay rapidly in simulation of the desired percussive tonal effect, and an output circuit for coupling said decaying tone signal to the sound producing device of said musical instrument.

References Cited in the file of this patent UNITED STATES PATENTS I-lanert Nov. 10, 1942 Wittenberg Nov. 27, 1951 OTHER REFERENCES 

